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Re: What are the criteria for "Zones"?

  • Subject: Re: What are the criteria for "Zones"?
  • From: "Randall M. Story" <story@caltech.edu>
  • Date: Wed, 22 May 2002 10:03:16 -0500 (CDT)

As people have mentioned, the USDA zone concept is really pretty limited. 
For example the foggiest parts of San Francisco, some of the hotter and
drier parts of Southern California as well as Miami Florida are all zone
10!!  Yet you certainly can't grow a Coconut Palm in San Francisco (or
anywhere in California that I know of), whereas a Dracula orchid that would
be very happy in coastal California would quickly fry in Florida. And on and

Even the heat index adds very little--there are parts of Florida and the
Arizona desert that have both the same heat and cold indexes, yet obviously
humidity, rainfall, temperature extremes, diurnal variation etc. are vastly

In the Western half of the U.S. there has been a different (and
unfortunately much more complicated zone system--24 zones!) devised by
Sunset Magazine/Books a number of years ago that takes into account things
such as humidity, ocean influence, etc.  Many of us out here are familiar
with it and it is very, very useful.   Recently it has been extended to the
rest of the U.S. (and Canada I think) creating yet more zones.  I don't
imagine they've extended it to Europe, yet I'm sure that the climate of
Ireland has much, much more in common with certain parts of coastal
Oregon/Washington (Sunset zone 5 maybe?) than it has with the equivalent
USDA zone anywhere else of the U.S.

Anyway, this is obviously really complicated, however someone has come up
with a system that makes sense for the U.S. at least.  Oh, and it doesn't
strictly depend on any particular Fahrenheit (or Celsius) number--you have
to look it up on a map.

I imagine that much of Europe could be approximated by one of these zones.
I don't know if anyone has tried.

html  for maps and descriptions of the zones for the western U.S.  I don't
know of any maps online for the rest of the country.


USDA zone 10/ Sunset zone 21

>From: "George R Stilwell, Jr." <grsjr@juno.com>
>To: Multiple recipients of list AROID-L <aroid-l@mobot.org>
>Subject: Re: What are the criteria for "Zones"?
>Date: Tue, May 21, 2002, 8:50 PM

> Ron,
> Zones have only to do with the mean low temperature. There is a new index
> to do with heat
> being dffered by the USDA. To answer your question, go to
> http://www.aroid.org/horticulture/zonemap/europe.html
> It's all self evident in this wonderful page.
> Ray
> GRSJr@worldnet.att.net
> ________________________________________________________________
> Juno offers FREE or PREMIUM Internet access for less!
> Join Juno today!  For your FREE software, visit:
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